Multivalent metal ion extraction using diglycolamide-coated particles

ABSTRACT

A separation medium, a method for using that separation medium and an apparatus for selectively extracting multivalent cations such as pseudo-lanthanide, prelanthanide, lanthanide, preactinide or actinide cations from an aqueous acidic sample solution is described. The separation medium is preferably free-flowing and comprises particles having a diglycolamide (DGA) extractant dispersed onto an inert, porous support.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 10/261,031 filedSep. 30, 2002.

TECHNICAL FIELD

The present invention is concerned generally with a method, separationmedium and apparatus for selectively extracting multivalent cations fromacidic aqueous solutions. More particularly, the invention is concernedwith a separation medium that is preferably free-flowing and iscomprised of a diglycolamide dispersed onto an inert substrate material,a method for using that separation medium and an apparatus forselectively extracting multivalent cations from an acidic aqueoussample.

BACKGROUND OF THE INVENTION

The wide-scale use of nuclear technology in power production and innuclear weapons manufacturing has necessitated the periodic monitoringof biological and environmental samples for the presence of selectedelements such as strontium (Sr), cerium (Ce), europium (Eu), actinium(Ac), thorium (Th), uranium (U,) neptunium (Np), plutonium (Pu),americium (Am), and curium (Cm), and for monitoring particular nuclidessuch as ⁹⁰Sr, ¹⁴⁴Ce, and ^(152,154)Eu. There is, therefore, a clear needfor an analytical procedure and methodology suitable for use in theroutine monitoring of persons whose activities expose them to the riskof internal contamination from these elements and for the determinationof the levels of radionuclides in various environmental samples (e.g.,soils, plants, natural waters, and waste streams). A number ofprocedures for the selective recovery of the above elements have beendisclosed.

U.S. Pat. No. 4,548,790 dated Oct. 22, 1985 describes a group of neutralbifunctional organophosphorus compounds broadly described as alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine oxides (hereinafterreferred to as CMPO) that are useful for the recovery of actinide andlanthanide cations from acidic solutions. The combination of the CMPOwith a phase modifier such as tri-n-butyl phosphate (hereinafterreferred to as TBP) in a normal paraffin hydrocarbon diluent isdescribed in U.S. Pat. No. 4,574,072 dated Mar. 4, 1986.

U.S. Pat. No. 4,835,107 dated Oct. 21, 1986 describes a method for theconcentration and separation of actinide cations from biological andenvironmental samples using CMPO and TBP in a chromatographic mode. TheCMPO/TBP chromatographic system was applied in the recovery andpurification of yttrium-90 for medical applications described in U.S.Pat. No. 5,368,736 dated Nov. 29, 1994. Other systems utilizingmonofunctional, as well as bifunctional, organophosphorus extractants inthe recovery of lanthanide and actinide cations from acidic media inboth the liquid-liquid extraction mode and in the extractionchromatographic mode are described in Kimura (1990) J. Radioanal. Nucl.Chem., 141, 295 and Ramanujam et al. (1995) Solvent Extr. Ion Exch.,13(2), 301–312.

U.S. Pat. Nos. 5,100,585, 5,110,474 and 5,346,618 by some of the presentinventors teach the manufacture and use of a chromatographic medium forselectively separating strontium or technetium cations from acidiccompositions from various sources. The solid phase chromatographicmedium made and used in those patents comprised a solution of a Crownether dissolved in a diluent that was slightly soluble or insoluble inwater, but capable of dissolving a substantial quantity of water, suchas octanol, which solution was itself dispersed onto a solid inert resinsubstrate material.

A few years after the filing of the applications that became the aboveU.S. patents, Benzi et al. (1992) J. Radioanal. Nucl. Chem., Letters,164(4):211–220 reported on the use of 18-Crown-6 (18C6),dibenzo-18-Crown-6 (DB18C6) and 24-Crown-8 (24C8) as well as open chainligands (podands) adsorbed on Amberlite® XAD-4 and XAD-7 resins orKieselgel as supports for removal of radium cations from aqueoussolutions. Those authors reported the supported crown ethers to beinefficient for that extraction, whereas the supported open chainligands were said to provide satisfactory distribution coefficients forthe removal of radium.

The above-noted patents of some of the present inventors provided alarge technological advance over the liquid-liquid separation techniquesthat preceded them, and from which their technical advance grew.However, the separation medium of those patents exhibited changes uponelution of the captured strontium cations that minimized theirusefulness for a subsequent separation, including loss of diluent to theeffluent medium. Still further, the amount of strontiumcation-extracting Crown ether present on any given support was limitedbecause of the presence of the diluent.

All of the prior methods suffer from one or more major disadvantages.Foremost among these is that the retention of the trivalent lanthanidesand actinides in acidic aqueous nitric and hydrochloric acid is limitingand the subsequent recovery in dilute acid is difficult, especially inthe case of tetra- and hexavalent actinides. In the chromatographicmode, low retention of the analyte in the column loading step results inits early breakthrough in the column effluent. Early breakthroughfrequently results in losses of analyte and insufficient purificationbecause of limited column rinsing capabilities.

In recent years, the wide-scale use of nuclear technology has alsoexpanded greatly in the field of medicine. The use of radioactivematerials in diagnostic medicine is now readily accepted because theseprocedures are safe, minimally invasive, cost-effective, and theyprovide unique information that is otherwise unavailable to theclinician. More recently, radioactive isotopes are being used to treatdisease as opposed to diagnosing disease. This technique is referred toas radioimmunotherapy (RIT). The U.S. Food and Drug Administration (FDA)has approved the use of the first RIT drug that relies on radioactivedecay to impart the cytotoxic effect to the disease site.

The FDA has mandated rigorous purity requirements for radionuclides usedfor therapeutic applications. Foremost among these requirements is highradionuclidic purity, which stems directly from the hazards associatedwith the introduction of long-lived or high-energy radioactiveimpurities into a patient. Chemical purity is also vital to a safe andefficient medical procedure because the radionuclide must generally bebonded to a biolocalizing agent prior to use. Biolocalizing agents haveextremely low capacities for metal ions and, therefore, the presence ofionic interferents can inhibit the uptake of the medically usefulradionuclide. Another critical factor in bonding the radionuclide to thebiolocalizing agent is obtaining the desired purified radionuclide in adilute ≦0.1 M acidic (usually HCl) aqueous solution. A number ofpseudo-lanthanide, prelanthanide, lanthanide, preactinide and actinidenuclides are candidates for use in radioimmunotherapy; for example,⁴⁷SC, ⁹⁰Y, ¹⁴⁹Pm, ¹⁵³Sm, ¹⁵³Gd, ¹⁶⁶Ho, ¹⁷⁷Lu, ²²⁵Ac, and ²⁵⁵Fm.

In related studies, Sasaki et al. [Sasaki et al. (2001) Solvent Extr.Ion Exch., 19(1):91–103; and Sasaki et al. (2002) Solvent Extr. IonExch., 20(1):21–34. See also the web site of the Japanese Atomic EnergyResearch Institute (JAERI) and Japanese Kokai No. 2002-1007 and No.2002-243890.] have published results on the liquid-liquid extraction oftrivalent lanthanides and tri-, tetra-, and hexavalent actinides withstructurally tailored diamides including selected diglycolamides.However, these studies were carried out using very dilute solutions ofthe extractants in nitrobenzene, chloroform, toluene, hexane, orn-dodecane. The aqueous phase was primarily nitric acid or 0.1 M sodiumperchlorate and, in the case of trivalent lanthanides and actinides,never exceeded 1 M in concentration. Extrapolation of these data to auseful extraction chromatographic system that can achieve the objectivescited herein cannot be done.

It has been demonstrated in related studies by Cortina et al. (1994)Solvent Extr. Ion Exch., 12(2):371–391, that quantitative predictions ofmetal ion uptake from liquid-liquid extraction data cannot be extendedto extraction chromatographic systems. These studies have shown that theselectivity order for the extraction of Cu and Cd (Cu greater than Cd)by bis-2-ethylhexyl phosphoric acid (HDEHP) is reversed for the solidsupported reagent. Studies by Miralles et al. (1992) Solvent Extr. IonExch. 10(1):51–68 and Casas et al. (1989) Polyhedron 8:2535 have shownthat the nature of the metal species extracted by HDEHP in toluene orparaffinic hydrocarbons is somewhat different from the same extractantsorbed on Amberlite® XAD-2. The extracted species is typically lesssolvated in the extraction chromatographic system than in theliquid-liquid extraction system. None of the above observations aresurprising because the film thickness of an extractant sorbed on aporous solid support having a surface area of 400 to 500 m²/g, forexample Amberchrom® CG-71, and containing 40 weight percent of anextractant with a density of 0.95 g/mL is only about 1 to 2×10⁻³ μm. Itis not, therefore, unexpected that the physical and chemical propertiesof the extractant and the concomitant extraction behavior in extractionchromatographic resins are different than in a liquid-liquid extractantsystem.

It would therefore be beneficial to provide a method, separation mediumand apparatus for separating multivalent cations from acidic aqueoussamples such as biological, commercial waste and environmental samplesthat do not exhibit the negative attributes of the prior technologies.The method, separation medium and apparatus of the present inventionthat are described hereinafter can overcome those negative attributes,while maintaining the previously achieved advances.

BRIEF SUMMARY OF THE INVENTION

The present invention contemplates a separation medium, an apparatus forcarrying out a separation such as a chromatographic column or cartridgecontaining the separation medium, and a method of using the separationmedium to separate a preselected multivalent metal cation such as apseudo-lanthanide [e.g., scandium(III) and yttrium(III)], aprelanthanide [lanthanum(III)], a lanthanide, a preactinide[actinium(III)] or an actinide cation, like trivalent americium (Am³⁺),yttrium (Y³⁺) and ytterbium (Yb³⁺) cations from other cations such asradium (Ra²⁺) cations present in an acidic aqueous solution. Acontemplated preselected multivalent metal cation, other than cadmium,typically has a crystal ionic radius in Ångstrom units of about 0.8 toabout 1.2. The separation medium comprises particles having adiglycolamide (DGA) extractant dispersed onto an inert, porous supportsuch as polymeric resin or silica particles. The separation medium ispreferably free of an organic diluent, although such a diluent can bepresent. A contemplated diglycolamide extractant corresponds instructure to Formula I

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido(hydrogen) or hydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 14to about 56 carbon atoms, and preferably about 16 to about 40 carbonatoms. More preferably each of R¹, R², R³ and R⁴ is a hydrocarbyl group.Most preferably, each of R¹, R², R³ and R⁴ is the same hydrocarbylgroup.

A method for separating a predetermined multivalent cation having acrystal ionic radius of about 0.8 to about 1.2 Ångstroms (Å) from anaqueous sample that contains additional mono- or multivalent metalcations, or both, is also contemplated. The aqueous sample also containsa salting out amount of one or more salting out agents for a neutralextractant such as high concentrations of nitric, hydrochloric,perchloric, or the like acids, or lithium nitrate, aluminum nitrate,lithium chloride or the like.

That method includes the steps of contacting an above-describeddiglycolamide-containing separation medium with an aqueous samplecontaining dissolved multivalent cations, including the predeterminedmultivalent cation. That contact is maintained for a time periodsufficient for the multivalent cations to be extracted from the samplesolution to the separation medium to form a solid phase-loadedseparation medium and a liquid phase multivalent cation-depleted sample.The solid and liquid phases are thereafter separated. The multivalentcation is thereafter preferably eluted by contacting the loadedseparation medium with water or dilute hydrochloric or nitric acids.

A separation apparatus for extracting multivalent cations from an acidicaqueous solution comprising the above separation medium in a supportvessel is also contemplated. A contemplated apparatus has a fluid inletand fluid outlet and one or more porous supports within the vessel formaintaining the separation medium in a desired position. A contemplatedsupport vessel is typically glass or plastic such as polyethylene orpolypropylene and is typically a chromatographic column or cartridge.

The present invention has several benefits and advantages.

One benefit of the invention is provision of a novel extractionchromatographic material for the separation of multivalent cations suchas those of Sc, Y, and lanthanides and actinides from biological,environmental and strongly acidic solution samples that contain othermetal cations and for use in nuclear medicine.

An advantage of the invention is the provision of an improved materialfor sorption of the above multivalent cations on a support from (a)strongly acidic nitric acid solution and the provision for recovering(stripping) those cations in dilute nitric acid solution, as well assorption from (b) strongly acidic hydrochloric acid solution and theprovision for recovering (stripping) of those cations in a dilutehydrochloric acid solution, and sorption from (c) from strongly acidicnitric acid solution and recovering those cations in a dilutehydrochloric acid solution.

Another benefit of the invention is the provision of an improvedmaterial for the sorption of those multivalent cations on an extractionmedium from an aqueous solution of nitrate or chloride salting out agentsalts such as lithium nitrate or chloride and aluminum nitrate andrecovering those cations in dilute hydrochloric and nitrate acidsolutions.

Another advantage of the present invention is the unexpected differencein D_(w) values observed for separation media between 0.1 and 3 M nitricor hydrochloric acids for particular trivalent metal cations when usinga diglycolamide extractant having four 2-ethylhexyl amido nitrogensubstituents as compared to a diglycolamide extractant having fourn-octyl substituents.

Still further benefits and advantages will be apparent to the skilledworker from the disclosure that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings forming a portion of this disclosure, and in which likelast two digit numbers indicate like structures,

FIG. 1 shows a schematic representation of a separation vessel useful inan embodiment of the invention;

FIG. 2 shows schematic representation of another separation vesseluseful in an embodiment of the invention;

FIG. 3 is a plot of D_(w) vs. [HNO₃] for uptake of Ba(II) (circles),Ce(III) (triangles), and Th(IV) (squares) by N,N,N′,N′-tetra-n-octyl-DGAresin, using a contact time of 1 hour at 25° C.;

FIG. 4 is a plot of D_(w) vs. [HCl] for uptake of Ba(II) (circles),Ce(III) (triangles), and Th(IV) (squares) by N,N,N′,N′-tetra-n-octyl-DGAresin, using a contact time of 1 hour at 25° C.;

FIG. 5 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) by N,N,N′,N′-tetra-n-octyl-DGAresin, using a contact time of 1 hour at 25° C.;

FIG. 6 is a plot of D_(w) vs. [HCl] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) by N,N,N′,N′-tetra-n-octyl-DGAresin, using a contact time of 1 hour at 25° C.;

FIG. 7 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) byN,N′-dihexyl-N,N′-dimethyl-DGA resin, using a contact time of 1 hour at25° C.;

FIG. 8 is a plot of D_(w) vs. [HCl] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) byN,N′-dihexyl-N,N′-dimethyl-DGA resin, using a contact time of 1 hour at25° C.;

FIG. 9 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) by N,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, using a contact time of 1 hour at 25° C.;

FIG. 10 is a plot of D_(w) vs. [HCl] for uptake of Ce(III) (circles) ,Eu(III) (squares), and Y(III) (triangles) by N,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, using a contact time of 1 hour at 25° C.; and

FIG. 11 is a chromatogram showing cpm/mL vs. Bed Volumes of Eluate forthe elution of Ra(II) (circles) and Ac(III) (triangles) on a 0.50 mL bedof N,N,N′,N′-tetra-n-octyl-DGA resin at 25° C.

DETAILED DESCRIPTION OF THE INVENTION

The present invention contemplates separation of a polyvalent metalcation from an aqueous sample composition. A contemplated multivalentmetal cation typically exhibits a valence of +3, +4 or +6, although some+2 cations can also be selectively separated. A more convenient way togenerically characterize a contemplated cation is by its valence inaqueous solution being +2 or greater and exhibiting a crystal ionicradius of about 0.8 to about 1.2 Ångstroms (Å), and more preferablyabout 0.9 to about 1.2 Å. All of the multivalent cations examined thusfar, with the exception of cadmium, that exhibit the above crystal ionicradius selectively bind to a contemplated separation medium.

Aside from cadmium, the size to capacity for separation on acontemplated separation medium works for the almost twenty multivalentcations studied thus far. Crystal ionic radii can be obtained from atable in the Handbook of Chemistry and Physics, 54^(th) ed., CRC Press,Cleveland Ohio, pages F-194-F195 (1964).

A contemplated multivalent cation is present in an aqueous sample thatcontains one or both of a monovalent cation and a multivalent cation.The aqueous sample also contains a salting out amount of one or moresalting out agents for a neutral extractant such as high concentrationsof nitric, hydrochloric, perchloric acids or the like or lithiumnitrate, aluminum nitrate, lithium chloride or the like, as are known inthe art. Thus, the salting out agent facilitates anion transport withthe separated multivalent cations from the aqueous phase to thecontemplated separation medium. Exemplary salting out amounts areillustrated hereinafter and include concentrations of acid of about 0.1M to concentrated, but are more usually about 4 to about 8 M, withnitric acid being a preferred salting out agent. Lithium nitrate andlithium chloride are typically used at about 0.5 M to their respectivesolubility limits, whereas aluminum nitrate is typically used at about0.2 M to its solubility limit.

A contemplated separation medium that can be used to bind multivalentcations such as the pseudo-lanthanide, prelanthanide, lanthanide,preactinide or actinide cations in the presence of one or both ofmultivalent and monovalent cations is comprised of a diglycolamide (DGA)extractant dispersed on inert solid phase support particles. Acontemplated diglycolamide extractant corresponds in structure toFormula I

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido(hydrogen) or hydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 14to about 56 carbon atoms. Preferably, R¹+R²+R³+R⁴ contains about 16 toabout 40 carbon atoms. More preferably each of R¹, R², R³ and R⁴ is ahydrocarbyl group. Most preferably, each of R¹, R², R³ and R⁴ is thesame alkyl, hydrocarbyl group.

The word “hydrocarbyl” is defined to include straight and branched chainaliphatic as well as alicyclic groups or radicals that contain onlycarbon and hydrogen. Thus, alkyl, alkenyl and alkynyl groups arecontemplated, as are aromatic hydrocarbons such as phenyl and naphthylgroups, and aralkyl groups such as benzyl and phenethyl groups. Where aspecific hydrocarbyl substituent group is intended, that group isrecited; that is, C₁–C₄ alkyl, methyl or dodecenyl. Exemplaryhydrocarbyl groups contain a chain of 1 to about 18 carbon atoms, andpreferably two to about 10 carbon atoms.

A particularly preferred hydrocarbyl group is an alkyl group.Illustrative alkyl groups include methyl, ethyl, propyl, iso-propyl,butyl, hexyl, octyl, nonyl and decyl groups. Particularly preferredalkyl groups are the n-octyl and the 2-ethylhexyl groups.

A contemplated separation medium comprises a diglycolamide extractantcoated on inert, solid phase support particles. Contemplated solid phasesupport particles are inert in that they do not react with the aqueousacid, such as the aqueous nitric acid that is present in a contemplatedseparation, or with the extractant.

A contemplated inert, porous support is itself preferably free-flowingwhen dry, and can be made of a variety of materials, including silicaand polymeric resin as known in the art for use in a chromatographiccolumn. By “free-flowing”, it is meant that the support and separationmedium are pourable particles that are free from substantial clumping.Thus, for example, a beaker of dry contemplated support particles or dryseparation medium particles pours much like dry silica gel powder usedfor column chromatography.

Exemplary silica-based support particles are available from SigmaChemical Co. (St. Louis, Mo.) under the designation controlled-poreglass and controlled-pore glyceryl-glass. These materials are availablein varying mesh sizes from 20–80 to 200–400 and in varying nominal poresizes from 75 through 3000 Å. Useful trimethylsilyl-bonded porous silicaparticles are available from Alltech Associates, Deerfield, Ill. Theseparticles have a nominal pore size of 300 Å and are available in 90–130,20–50 and 35–70 micron diameters.

Exemplary useful polymeric resins include the Amberlite® polyaromaticresins such as those sold under the designations XAD-4, XAD-8, XAD-11and XAD-16, and the acrylic resin sold under the designation XAD-7 byRohm and Haas Co., Philadelphia, Pa. and are available in 20–60 meshsize. These resin particles are said to have the following average porediameters and surface areas: XAD-4 40 Å and 725 m²/g; XAD-7 90 Å and 450m²/g; XAD-16 100 Å and 800 m²/g, and are referred to in the art asmacroreticular resins. Illustrative spherical rigid bead macroreticularAmberchrom® resins such as those sold under the designations CG-161,CG-300, CG-100 for styrene/divinyl benzene-containing materials, andCG-71 for a methacrylate/dimethacrylate-containing material are alsouseful. These latter resin particles are commercially available fromTosoHaas, Montgomeryville, Pa. Each of the latter four resins isavailable in three particle size ranges: “s” or superfine at 20–50 μm,“m” or medium at 50–100 μm, and “c” or coarse at 80–160 μm. Typicalresin particles are reported to have the following average pore sizesand surface areas: CG-161 150 Å and 900 m²/g; CG-300 300 Å and 700 m²/g;CG-1000 1000 Å and 200 m²/g; and CG-71 250 Å and 500 m2/g. It isunderstood that the Amberlite® XAD-7 and Amberchrom® CG-71 arechemically similar materials, as are Amberlite® XAD-4 and Amberchrom®CG-161.

A contemplated polymeric resin support is typically sufficientlyhydrophilic and wettable that when placed in distilled water and shaken,the resin sinks rather than floats. A more quantitative determination ofa satisfactory support can be found in the water regain values discussedin Parrish (1977) Anal. Chem., 49(8):1189–1192 and Parrish (1965) J.Appl. Chem. (London), 15:280–288. Using water regain values, acontemplated resin exhibits a water regain value greater than about0.75, and less than about 3.5. A preferred resin exhibits a water regainvalue of about 1 to about 2.5, and more preferably about 1.75 to about2.25.

A contemplated support has sufficient porosity that it can adsorbdiglycolamide extractant loaded (coated) in an amount of about 3 toabout 50 weight percent of the total separation medium weight and stillremain free-flowing when dry. The diglycolamide extractant is morepreferably present at about 10 to about 40 weight percent of theseparation medium, and more preferably still at about 20 to about 40weight percent in the absence of diluent. When diluent is present, thediglycolamide portion can be about 3 to about 30 weight percent of theseparation medium.

A contemplated support is also preferably particulate. By “dry”, it ismeant that the separation medium loses less than about 5 weight percentafter being held at a temperature of 50° C. at a pressure of 0.1 mm ofmercury for 24 hours.

More specifically, a preferred solid phase separation medium iscomprised of free-flowing particles that contain about 40 weight percentN,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA) extractant coated onAmberchrom -CG71, and is referred to as Yttrium Resin. The Yttrium Resinis now commercially available from Eichrom Technologies, Inc.

The diglycolamide extractant can be present in a contemplated extractionmedium alone or it can be dissolved in an organic diluent. When adiluent is present, the extraction medium particles may adhere to eachother (cohere), rather than being free flowing as are particles of drysand, which is preferred. A contemplated separation medium is preferablyfree of an organic diluent, and preferably free of a diluent that is (i)insoluble or has limited (sparing) solubility in water and (ii) capableof dissolving a substantial quantity of water.

The amount of diglycolamide extractant in the diluent can vary dependingupon the particular diglycolamide utilized. For example a concentrationof about 0.1 to about 0.5 M of the tetraoctyl form in the diluent issatisfactory, with about 0.2 M being preferred. Concentrations aboveabout 0.5 M of the diglycolamide in the diluent tend not improvemultivalent metal ion recovery. Other diglycolamide derivatives can bepresent at about 0.1 to about 1.5 molar in the diluent.

The diluent is an organic compound that has a relatively high boilingpoint; that is, about 170 degrees to about 220 degrees C at atmosphericpressure, limited or no solubility in water; that is, about 0.5 weightpercent or less, and in which the diglycolamide is soluble. Some of thediluents contemplated can dissolve about 0.5 to about 6.0 M of water.

Particularly preferred diluents are hydrocarbons such as decane,dodecane, decalin, diethylbenzene and diisopropylbenzene. Otherillustrative diluents include alcohols, ketones, carboxylic acids,esters and nitroaromatics such as nitrobenzene. Suitable alcoholsinclude 1-octanol, 1-heptanol and 1-decanol. The carboxylic acidsinclude octanoic acid, heptanoic and hexanoic acids. Ketones that meetthe criteria can be either 2-hexanone or 4-methyl-2-pentanone, whereasthe esters include butyl acetate and amyl acetate.

The extractant such as N,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA)and similar tetraalkyl diamides dissolved in a water-insoluble organicsolvent such as nitrobenzene, chloroform, toluene or an alkane such asn-hexane or n-dodecane reported to be useful for the liquid/liquidextraction of lanthanide and actinide cations from aqueous nitric andperchloric acid solutions are known. [Sasaki et al. (2001) Solvent Extr.Ion Exch., 19(1):91–103; and Sasaki et al. (2002) Solvent Extr. IonExch., 20(1):21–34. See, also the web site of the Japanese Atomic EnergyResearch Institute (JAERI) and Japanese Kokai No. 2002-1007 and No.2002-243890.] In those studies, the synthesis ofN,N,N′,N′-tetra-(2-ehtylhexyl) diglycolamide not reported nor was thecation partitioning behavior of this extractant ever reported by theseauthors. That is a new compound.

The extractant such as N,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA)can be mixed with a lower boiling organic solvent such as methanol,ethanol, acetone, diethyl ether, methyl ethyl ketone, hexanes, ortoluene and coated onto an inert support, such as glass (silica) beads,polypropylene beads, polyester beads, or silica gel.

A method for separating a preselected multivalent lanthanide or actinidecation from an aqueous sample containing additional polyvalent metalcations is contemplated. That method includes the steps of contacting anabove-described separation medium with an acidic aqueous samplecontaining dissolved multivalent cations, including the predeterminedlanthanide or actinide cation. That contact is maintained for a timeperiod sufficient for the multivalent lanthanide or actinide cations tobe extracted from the sample solution to the separation medium to form asolid phase loaded separation medium and a liquid phase multivalentlanthanide or actinide cation-depleted sample. The solid and liquidphases are thereafter separated. The lanthanide or actinide cation isthereafter preferably eluted from the loaded separation medium bycontacting the loaded separation medium with water or dilutehydrochloric acid. The contact is typically carried out at an aciditynear the maximum for the cation(s) to be separated (extracted), such asat an acid concentration near that at which the separation mediumreaches maximal extraction.

Extraction of the lanthanide or actinide cations from the solution tothe separation medium to form a solid phase loaded separation medium istypically a rapid event. Thus, gravity feed of a lanthanide or actinidecation-containing aqueous sample solution through a typicallydimensioned chromatographic column containing the separation medium withlittle retardation of the flow rate typically provides a sufficientcontact maintenance time. Swirling of the sample solution and separationmedium for a few minutes in a flask or beaker is also typicallysufficient contacting.

Separation of the solid and liquid phases is also readily achieved.Where a column or cartridge is used as the separation apparatus, passageof the liquid phase lanthanide or actinide cation-depleted sample out ofthe vessel is sufficient to effect the desired solid/liquid phaseseparation. Where a beaker, flask or other vessel is used for theseparation, simple decantation can be used to effect the separation ofphases. One can also use aqueous lithium nitrate, lithium chloride oraluminum nitrate in a wash or rinsing step to assist in elutinginterfering cations that may be maintained in the load solution presentin the interstices between particles.

In preferred practice, the desired lanthanide or actinide cations areselectively eluted from the loaded separation medium by contacting theloaded separation medium with an aqueous solution having a pH value ofabout 1 or less, or with plain distilled or deionized or even tap water.The elution solution need not be distilled or deionized water, althoughsuch water is preferred. Typically, aqueous 0.1 M HCl is utilized toelute lanthanide or actinide cations from the separation medium. Theconcentration of nitrate anions is also preferably less than or equal toabout 0.1 molar.

The contacting of the separation medium with the aqueous acidiclanthanide or actinide cation-containing sample can be carried out in anopen or closed vessel in which the solid and liquid are swirled orstirred together. It is more preferred, however, that that contactingstep be carried out in a below-described support vessel such as achromatographic separation column or cartridge by passing the aqueousacidic sample solution through the vessel, and that the preferredelution of lanthanide or actinide cations be carried out by passingwater or dilute hydrochloric acid (at a concentration of about 0.1 M orless) through the loaded separation medium in the support vessel.

An apparatus for separating lanthanide or actinide cations such asyttrium or actinium cations from an acidic aqueous solution comprisingthe above separation medium in a support vessel is also contemplated. Acontemplated support vessel is typically glass or plastic such aspolyethylene or polypropylene and is typically a chromatographic columnor cartridge. A contemplated vessel can include one or more inlets,outlets, valves such as stopcocks and similar appendages.

One contemplated support vessel is cylindrical and has an inlet forreceiving an aqueous sample solution prior to contact of the samplesolution with the contained separation medium and an outlet for theegress of water or other liquid after contact with the medium. When thesupport vessel is a glass or plastic chromatographic column orcartridge, the vessel can contain appropriate valves such as stopcocksfor controlling aqueous flow, as are well-known, as well as connectionjoints such as Luer fittings. The inlet for receiving an aqueous liquidsample solution and outlet for liquid egress can be the same structureas where a beaker, flask or other vessel is used for a contemplatedseparation process, but the inlet and outlet are typically different andare separated from each other. Usually, the inlet and outlet are atopposite ends of the apparatus.

FIG. 1 provides a schematic drawing of one preferred separationapparatus. Here, the separation apparatus 10 is shown to include asupport vessel as a column 12 having an inlet 26 and an outlet 28 forliquid such as water. The outlet has an integral seal and is separablefrom the seal at a frangible connection 32. The separation apparatus 10contains one or more flow-permitting support elements. In oneembodiment, a frit 22 supports separation medium 16, and an upper frit18 helps to keep the separation medium in place during the introductionof an influent of aqueous sample or eluting solution. Contemplated fritscan be made of glass or plastic such as high-density polyethylene(HDPE). A HDPE frit of 35–45 μm average pore size is preferred. Acontemplated apparatus can also include a stopcock or otherflow-regulating device (not shown) at, near or in conjunction with theoutlet 28 to assist in regulating flow through the apparatus.

An above-described chromatographic column is typically offered for salewith a cap (not shown) placed into inlet 26 and snap-off (frangible)tube end 30. The separation medium in such a column is typically wet andequilibrated with about 0.05 to about 0.5 N HNO₃. It is preferred thatthe average diameter of separation medium particles be about 100 toabout 150 μm when a chromatographic column separation apparatus isprepared and used.

FIG. 2 provides a second schematic drawing of another preferredseparation apparatus. Here, the separation apparatus 110 is shown toinclude a support vessel as a cartridge 112 having an inlet 126 and anoutlet 128 for liquid such as water. A cap 124 is preferably integrallymolded with the inlet 126. The outlet 128 is preferably integrallymolded with the cartridge 112. The separation apparatus 110 contains aporous support such as a frit 122 that supports separation medium 116.An upper porous support such as a frit 118 helps to keep the separationmedium in place during the introduction of an influent aqueous sample oreluting solution. A contemplated apparatus can also include a stopcockor other flow-regulating device (not shown) at, near or in conjunctionwith the outlet 128 to assist in regulating flow through the apparatus.

A contemplated cartridge such as a separation vessel of FIG. 2 istypically provided with the separation medium in a dry state, or atleast not wet with aqueous nitric acid. In addition, inlet 126 andoutlet 128 are preferably standard fittings such as Luer fittings thatare adapted for easy connection to other standard gas and/or liquidconnections. It is also preferred that the average diameter ofseparation particles be about 50 to about 100 μm when a cartridgeseparation apparatus is prepared and used.

One contemplated separation apparatus such as that of FIG. 1 can bereadily prepared by slurrying the separation medium in water oracidified water such as 0.5 normal nitric acid. The slurry is added ontoa flow-permitting support element such as a frit in a verticallyoriented support vessel such as a column. The separation medium ispermitted to settle under the force of gravity and can be packed moredensely using vibration, tapping or the like. Once a desired height ofseparation medium is achieved, any excess liquid is removed as byvacuum, a second flow-permitting element such as another frit isinserted into the column above the separation medium and the cap isadded.

To prepare another chromatographic column that can be used for acontemplated separation, a portion of separation medium prepared asdiscussed above is slurried in 0.5 M nitric acid and aliquots of thatslurry are transferred under nitrogen pressure to a 10 cm long glassBio-Rad® column (1.4 mm inside diameter) equipped with polypropylenefittings manufactured under the trademark “Cheminert” by Chromatronix,Inc., Berkeley, Calif. When the desired bed height is reached(corresponding to a bed volume of about 0.6 cm³), the separation mediumis resettled by backwashing. The separation medium is then rinsed withseveral bed volumes of 0.5 M nitric acid.

Chromatographic columns can similarly be prepared in other vessels suchas 23 cm long glass Pasteur pipettes having a small glass wool plug(porous support) in the bottom and a layer of 80/100 mesh glass beads ontop of the separation medium to prevent disruption of the bed by sampleintroduction. Because these pipettes lack a liquid-holding reservoir,sample solutions are introduced using a small polyethylene funnelattached to the top of the pipette via a short length of vinyl tubing.See, Dietz et al. (1996) J. Chem. Ed., 73(2):182–184.

A separation vessel shown in FIG. 2 can be prepared by adding apredetermined weight of dry separation medium to the cartridge 112containing molded outlet 128 and support frit 122. The thus filledcartridge is vibrated in a vertical orientation to achieve a constantheight for the separation medium bed, the upper porous support 118 isinserted, and the cap 124 containing molded fluid inlet 126 is placedonto the device.

Partition ratios for multivalent cations are measured radiometricallyusing conventional procedures, and all measurements are performed at 23±2° C. Gamma and beta counting are performed on a Packard® Cobra GammaCounter and a Packard® Model 2200 Liquid Scintillation Counter,respectively. Assessment of non-radioactive elements is performed usingwell-known inductively-coupled plasma atomic emission spectroscopy.

The DF value for a given step is multiplied with the DF value for thenext step or, when represented using exponents, the DF value exponentsare added for each step. A DF value of about 10¹⁰ is about the largestDF that can be readily determined using typical radioanalyticallaboratory apparatus.

The decontamination factor (DF) is defined using the following equation:

${DF} = \left( \frac{\frac{\lbrack{Analyte}\rbrack_{effluent}}{\lbrack{Impurity}\rbrack_{effluent}}}{\frac{\lbrack{Analyte}\rbrack_{influent}}{\lbrack{Impurity}\rbrack_{influent}}} \right)$

For a system at radioactive steady state (e.g., ²²⁹Th and its daughtersincluding ²²⁵Ac, ²²⁵Ra and ²¹³Bi), the denominator is about 1. Thismeans a DF value can be approximated by examining the stripping peak ina chromatogram and dividing the maximum cpm/mL for the analyte (i.e.,the desired ²²⁵Ac and ²²⁵Ra daughter radionuclides) by the activity ofthe impurities (i.e., ²²⁹Th parent).

Alternatively, the DF value can be calculated by taking the ratio of thedry weight distribution ratios (D_(w)) for an analyte and impurity. Thedry weight distribution ratio is defined as:

$D_{w} = {\left( \frac{A_{o} - A_{f}}{A_{f}} \right)\left( \frac{V}{m_{R} \cdot \left( {\%\mspace{14mu}{{solids}/100}} \right)} \right)}$where A_(o)=the count rate in solution prior to contact with the resin,A_(f)=the count rate in solution after contact with resin, V=volume (mL)of solution in contact with resin, m_(R)=mass (g) of wet resin, and the% solids permits conversion to the dry mass of resin. The sorption ofvarious radioisotopes from nitric acid solution by a separation mediumis initially measured by contacting a known volume (typically 1.0 mL) ofa spiked acid solution of appropriate concentration with a known mass ofmedium. The ratio of the aqueous phase volume (mL) to the mass of thechromatographic materials (g) ranges from 70 to 180. (This ratio isdetermined primarily by the need to produce an easily measured decreasein the aqueous activity by contact with the medium.) Althoughequilibrium is generally reached in less than 20 minutes, a 1 hourmixing time is normally employed.

The D_(w) values can be converted to the number of free column volumesto peak maximum (i.e., the resin capacity factor), k′, by dividing byapproximately 2.19. This factor includes the conversion of D_(w) to D (avolume partition ratio) and the value of the ratio of the volume ofstationary phase (v_(a)) to the volume of mobile phase (v_(m)) ,v_(a)/v_(m), typically observed for chromatographic columns packed withthe Strontium-selective resin (Eichrom Technologies, Inc.). (The term“stationary phase” refers to the volume of liquid extracting solutioncontained in the pores of the support.)

Assuming that the “influent” is at radioactive steady state (making thedenominator for DF unity), the ratio of D_(w) values foranalyte/impurity are:

${DF} = \frac{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{analyte}/\left( \frac{V}{m_{R} \cdot \left( {\%{\mspace{11mu}\;}{{solids}/100}} \right)} \right)}{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{impurity}/\left( \frac{V}{m_{R} \cdot \left( {\%\mspace{14mu}{{solids}/100}} \right)} \right)}$which simplifies after cancellation to:

${DF} = \frac{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{analyte}}{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{impurity}}$where A_(o), A_(f), V, m_(R) and % solids are as previously defined.These ratios of activities are proportional to the molar concentrationscited elsewhere in the definition of DF.

EXAMPLE 1 Synthesis of N,N,N′,N′-Tetra-n-octyl-diglycolamide (TO-DGA)

The synthesis of the TO-DGA is comparatively straightforward usingcommercially available reactants, requiring only 1–2 reaction steps, andeasy purification by an extractive process. The overall synthesis andpurification can be accomplished in less than six person-hours withabout a 90% overall yield. An illustrative, not yet optimized synthesisprocedure for the production of 60 grams of the TO-DGA is detailedbelow.

All chemicals were purchased from Aldrich Chemical Co., Milwaukee, Wis.,and were used as received, except for the triethylamine that was freshlydistilled from calcium hydride before use. All glassware was oven-driedprior to use and the reaction was carried out at ambient temperature. Apositive pressure inert atmosphere of nitrogen was maintained with alatex balloon and the reaction mixture was stirred magnetically.Reactions on a larger scale require mechanical stirring because of thelarge amount of precipitate that formed.

A 500-mL single-neck round bottom flask was charged with drytetrahydrofuran (THF) (120 mL) and diglycolyl chloride (15.0 mL, 126mmol). The flask was partially immersed in a H₂O bath to dissipate heatfrom the mild exotherm. A dropping funnel was charged with dioctylamine(57.4 g, 238 mmol) and triethylamine (37.2 mL, 265 mmol) in THF (60 mL).

The amine solution was added drop-wise to the magnetically stirredreaction mixture over a period of about 1.5 hours. A white precipitateof triethylammonium chloride immediately formed upon combining thesolutions. After addition of the amine solution was complete, thedropping funnel was rinsed with an additional 10 mL THF, which was addedto the reaction mixture. The mixture was stirred for an additional 1hour, after which 10 mL H₂O was added. The THF was subsequently removedby rotary evaporation.

To the pasty yellow residue was added 100 mL H₂O, creating a viscousorange upper phase and a colorless, cloudy lower phase. The phases wereseparated in a separatory funnel and the lower phase was extracted twicewith 10 mL petroleum ether. The petroleum ether washes were added to theinitial upper phase that was extracted with 15 mL H₂O, 2×15 mL 1 M HCl,15 mL H₂O, and 20 mL 5% (w/v) NaHCO₃. Both resulting phases were cloudyorange.

After settling for about 18 hours, the two phases had not changed inappearance. The upper phase was extracted five times with 20 mL 5%NaHCO₃. The lower phases appeared to be emulsions after extraction andwere discarded. The upper phase was extracted with 10 mL 1 M HCl, 2×10mL H₂O, and 25 mL brine, dried over anhydrous MgSO₄, filteredgravitationally through fluted paper, and concentrated by rotaryevaporation. Yield: 62.92 g (91%) orange oil.

Similar preparations were carried out using other amines, includingbis(2-ethylhexyl)-amine, and a repeat synthesis was carried out usingdioctylamine. The results of those syntheses and initial analytical dataare provided below in Table 1.

TABLE 1 Analytical Data for Diglycolamides of the Formula RR′NC (O)CH₂OCH₂ C (O) NRR′ Appear- Yield R R′ ance % NMR or MS Octyl OctylOrange oil 94 ¹H NMR: 4.307 (s, 4H); 3.291 (t, 4H, J=8 Hz); 3.177 (t,4H, J=8 Hz); 1.519 (m, 8H); 1.272 (br, 40H); 0.885 (t, 6H, J=6 Hz);0.876 (t, 6H, J=6 Hz) LC-MS: 3.6 min (2%, m/z 358.2, calcd for dioctyldiamide C₂₀H₄₀N₂O₃ · H⁺: 357.31); 4.06 min (1%, m/z 469.3, calcd fortrioctyl diamide C₂₈H₅₆N₂O₃ · H⁺: 469.44); 4.53 min (96%, m/z 581.4,calcd for tetraoctyl diamide C₃₆H₇₂N₂O₃ · H⁺: 581.56) 2-Ethyl- 2-Ethyl-Light 94 ¹H NMR: 4.330 (s, 4H); 3.37 hexyl hexyl yellow oil (m, 4H);3.043 (d, 4H, J=7 Hz); 1.669 (m, 3H); 1.560 (m, 3H), 1.25 (m, 30H); 0.88(m, 24H) LC-MS: 4.47 min (91%, m/z 581.4, calcd for tetra-(2-ethylhexyl)diamide C₃₆H₇₂N₂O₃ · H⁺: 581.56), 5.50 min (9%, m/z 920.4).Hexyl Methyl Yellow oil 84 ¹H NMR: 4.314 (s, 4H); 4.293 (s, 2H); 3.351(t, 4H, J=8 Hz); 3.23 (t, 4H, J=8 Hz); 2.962 (s, 6H); 2.920 (s, 6H);1.529 (m, 8H); 0.885 (m, 12H) ESI-MS: 329.6 calcd for C₁₈H₃₆N₂O₃ · H⁺:329.28); 351.7 (calcd for C₁₈H₃₆N₂O₃ · Na⁺: 351.26); 680.0 (calcd for2[C₁₈H₃₆N₂O₃] · Na⁺: 679.97) Decyl Decyl Waxy 72 ¹H NMR: 4.300 (s, 4H);3.289 white (t, 4H, J=7.7 Hz); 3.171 solid (t, 4H, J=7.7 Hz); 1.517 (m,8H); 1.26 (br, 56H); 0.883 (t, 6H, J=7 Hz); 0.878 (t, 6H, J=7 Hz) LC-MS:3.3 min (2%, m/z every 44 amu from 532.2 to 796.2); 4.6 min (2%, m/z581.4); 5.4 min (95%, m/z 693.5, calcd for tetradecyl diamide C₄₄H₈₈N₂O₃· H⁺: 693.69). Octyl H White 93 6.28 (br, 2H); 4.041 (s, 4H); flakes3.311 (q, 4H, J=6.5 Hz); 1.54 (m, 4H); 1.3 (m. 20H), 0.883 (t, 6H, J=7Hz) LC-MS: 3.5 min (98%, m/z 357.2, calcd for dioctyl diamide C₂₀H₄₀N₂O₃· H⁺: 357.31), 5.3 min (2%, m/z 693.5).

NMR spectra were recorded in chloroform-d with tetramethylsilaneinternal reference using Varian Inova 400 MHz or 500 MHz spectrometers.MS was carried out using a PE Sciex API 150 EX Mass Spectrometer withESI probe, positive ion detection. LC-MS was carried out using aPhenomenex LUNA-C18-2 column, 100×4.6 mm, 20% water/80% acetonitrileeluent. Peak detection was by mass spectrometry using atmosphericpressure chemical ionization (APCI) and an ion trap mass spectrometer,positive ion detection.

EXAMPLE 2 Preparation of Yttrium (TO-DGA) Resin

The separation medium used herein containing TO-DGA was prepared using ageneral procedure described previously for another separation medium[Horwitz et al., Anal. Chem. 1991, 63, 522–525]. A portion of TO-DGA(4.0 g) was dissolved in about 30 mL of CH₃OH and combined with 50–100μm Amberchrom®-CG71 particles (6.0 g) in about 20 mL of CH₃OH. Themixture was rotated at about 50° C. on a rotary evaporator for about 30minutes, after which the CH₃OH was vacuum distilled. After the bulkCH₃OH had been distilled, the free flowing resin was rotated under fullvacuum at about 40–50° C. for another 30 minutes to remove residualCH₃OH. The resulting solid is referred to as Yttrium Resin andcorresponds to 40% (w/w) loading of TO-DGA on 50–100 μm Amberchrom®-CG71particles.

EXAMPLE 3 Extraction Studies with Yttrium Resin

The TO-DGA molecules behave as neutral extractants; that is, soluteloading occurs at high acid (e.g., nitric (HNO₃) or hydrochloric (HCl)acids) or salt concentrations (e.g., lithium nitrate (LiNO₃), lithiumchloride (LiCl) or aluminum nitrate [Al(NO₃)₃] and stripping isaccomplished using dilute acid or salt solutions. One particularlynoteworthy characteristic of the TO-DGA resin, shown below, is the highuptake of polyvalent cations from 0.1–5 molar HNO₃ and the efficientstripping of these same cations using dilute (about 0.5 M or less) HCl.The elution behavior of several tri-, tetra-, and hexavalent cations onthe separation medium prepared (chromatographic material) usingN,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA) extractant describedbefore are shown below in Table 2.

TABLE 2 Elution Behavior of Selected Cations on TO-DGA Resin* Percent ofTotal Fraction Bed Volume Al(III) Y(III) Th(IV) U(VI) Load(0.5 M HNO₃)2.0 66 0 0 0 Rinse 2.0 28 0 0 75 (0.1 M HNO₃) 2.0 0 0 0 8.4 2.0 0 0 0 02.0 0 0 0 0 2.0 0 0 0 0 Strip 2.0 0 24 78 0 (0.1 M HCl) 2.0 0 76 16 02.0 0 0 0 0 2.0 0 0 0 0 2.0 0 0 0 0 *Bed volume = 0.5 mL; Flow rate =0.1 mL/minute for load, rinse, and strip

The negligible affinity of the TO-DGA resin for Al permits convenientpurification of analytes from this frequently encountered matrix cation.The elution of U in 0.1 M HNO₃ while Th is retained is noteworthy, asthis separation can be accomplished at significantly lower acidconcentrations than employed using conventional anion exchange resins orquaternary alkylamine extraction chromatographic materials. Theextraction behavior of the TO-DGA resin is useful in the separation andconcentration of tri-, tetra-, and hexavalent cations and in thecrossover from nitrate to chloride media (the medium of choice formedical applications).

Data relevant to the use of the TO-DGA resin separation media includes:

-   TO-DGA Formula Weight=580.98-   Column Capacity:    -   40% (w/w) TO-DGA on Amberchrom®-CG71    -   Bed density=0.35 g/mL of bed    -   0.40×0.35=0.140 g of TO-DGA/mL of bed or    -   0.241 mmol of TO-DGA/mL of bed-   Column capacity for Sr²⁺ and Ra²⁺    -   Assume three TO-DGA per Sr²⁺ or Ra²⁺    -   0.0803 mmol/mL of bed-   Column capacity for Yb³⁺:    -   Assume 4 DGA per Yb³⁺:    -   0.24/4=0.06 mmol of Yb³⁺/mL of bed    -   11 mg of Yb³⁺/mL of bed

EXAMPLE 4 Uptake Results

Initial studies focused on the N,N,N′,N′-tetra-n-octyl derivative ofdiglycolamide (DGA), and FIG. 3 shows the batch uptake results forBa(II), Ce(III), and Th(IV) as a function of nitric acid concentration([HNO₃]) on a separation medium containing 40% (w/w)N,N,N′,N′-tetra-n-octyl-DGA on Amberchrom®-CG71 particles as an inertresin support. The partitioning of Ce(III) and Th(Iv) increase steadilyup to about 3.0 M HNO₃, where the dry weight distribution ratio (D_(w))for Ce(III)=4.5×10³ and for Th(IV) D_(w)=1.0×10⁴.

Recovery of Ce(III) from the N,N,N′,N′-tetra-n-octyl-DGA resin can bereadily accomplished using dilute HCl, as shown in FIG. 4. The D_(w)values for Ce(III) decrease to less than 10 by 2.0 M HCl, whereas thepartitioning of Th(IV) plateaus in the D_(w)=10–20 range belowapproximately 0.50 M HCl. Barium(II) is not retained to any significantextent by N,N,N′,N′-tetra-n-octyl-DGA in either HNO₃ or HCl solutions,as shown in FIGS. 3 and 4.

EXAMPLE 5 Steric Effects on Diglycolamide Uptake

Additional studies targeting an understanding of the influence of alkylgroup size on trivalent cation selectivity exhibited by separation mediacontaining 40% by weight of the N,N,N′,N′-tetra-n-octyl,N,N′-di-n-hexyl-N,N′-dimethyl, or N,N,N′,N′-tetra-(2-ethylhexyl)derivatives of DGA were undertaken.

The N,N′-di-n-hexyl-N,N′-dimethyl-DGA is expected to have diminishedsteric impact on the coordination and extraction mechanisms because ofthe shorter alkyl chains compared to N,N,N′,N′-tetra-n-octyl-DGA. Suchshort alkyl groups may result in diminished utility as an extractionchromatographic material, however, as the decreased lipophilicity of theextractant is anticipated to give a separation medium that is lessstable with respect to extractant leaching during column chromatographicoperations.

The N,N,N′,N′-tetra-(2-ethylhexyl)-substituted DGA permits a moredetailed investigation of steric crowding as the four 2-ethylhexylsubstituents are closer to the carbonyl oxygen donor sites that interactwith the cation during the extraction process. The effects of the2-ethylhexyl substituent on the selectivity of organophosphorus acidextractants is well-known, [Sekine et al. Solvent Extraction Chemistry:Fundamentals and Applications; Marcel Dekker: New York, 1977; andRydberg et al. Eds. Principles and Practices of Solvent Extraction;Marcel Dekker: New York, 1992] and N,N,N′,N′-tetra-(2-ethylhexyl)-DGArepresents an interesting neutral extractant for the study of trivalentlanthanide separations as N,N,N′,N′-tetra-n-octyl-DGA already hasdisplayed considerable selectivity for heavy lanthanide cations overlight lanthanide cations in various solvent extraction studies. [Sasakiet al. (2001) Solvent Extr. Ion Exch., 19:91–103; and Sasaki et al.(2002) Solvent Extr. Ion Exch., 20:21–34.]

The partitioning of Ce(III), Eu(III), and Y(III) (the latterrepresentative of a heavy lanthanide cation) byN,N,N′,N′-tetra-n-octyl-DGA resin as a function of [HNO₃] is shown inFIG. 5. The acid dependencies increase steadily from 0.010 M HNO₃ toapproximately 3.0 M HNO₃, where some leveling is observed for theheavier lanthanide cations. The intralanthanide separation factorsappear to maximize around 1.0 M HNO₃, with a separation factor forY(III) from Ce(III) (S^(y) _(ce)=(D_(w) for Y(III))/(D_(w) for Ce(III)))of 69 and S^(Y) _(Eu) of 5.8.

Because the partitioning of Eu(III) and Y(III) is considerable (i.e.,D_(w) is about 10³ or more) at the comparatively low concentration of0.10 M HNO₃, stripping of these solutes from theN,N,N′,N′-tetra-n-octyl-DGA resin is not practical using dilute HNO₃.FIG. 6 shows the dependence of D_(w) vs. [HCl], and it is evident thatCe(III) and Eu(III) can be readily stripped using less than 1.0 M HCl,whereas Y(III) plateaus in the D_(w)=30–80 range below 1.0 M HCl.Related chromatographic experiments have shown that Y(III) isefficiently eluted using 0.10 M HCl.

FIG. 7 shows the partitioning of Ce(III), Eu(III), and Y(III) byN,N′-di-n-hexyl-N,N′-dimethyl-DGA resin as a function of HNO₃concentration. The acid dependencies start at unusually high D_(w)values of greater than 10³ and increase with an approximate unit slope,which is unusual as the extraction of trivalent cations by neutralextractants typically afford slopes of approximately three to meetelectroneutrality requirements.

The absence of a clear dependence on [HNO₃] indicates that stripping theloaded solutes from N,N′-di-n-hexyl-N,N′-dimethyl-DGA resin with HNO₃ isnot practical in a commercial setting, and the prospects of strippingwith HCl are equally poor in view of the data in FIG. 8. Shown here as afunction of [HCl] are the D_(w) values for Ce(III), Eu(III), and Y(III),which do not decrease appreciably (about 200–3000) over the 0.010–8.0 MHCl range to afford any useful elution conditions.

Further, any selectivity between the lanthanide analytes has disappearedand the comparatively flat acid dependencies raise questions about themechanism of extraction. Such properties also point to a unique utilityof this separation medium to extract these cations as a single useseparation medium that can extract selected cations and be discarded orotherwise treated as a concentrated waste because the solutes cannot beconveniently stripped by adjusting either the HNO₃ or HCl acidconcentration. Thus, a mixture of trivalent and lower valent materialscan be contacted with the separation medium resin and the trivalentcations trapped on the resin.

The N,N,N′,N′-tetra-(2-ethylhexyl)-DGA molecule introduces alkyl groupbranching and comparatively more steric hindrance near the site ofcation coordination. The data of FIG. 9 show the dependence of D_(w) forCe(III), Eu(III), and Y(III) vs. [HNO₃] forN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, in which a greater aciddependence of D_(w) is observed than for the N,N,N′,N′-tetra-n-octylderivative (FIG. 5).

For example, N,N,N′,N′-tetra-n-octyl-DGA exhibits a D_(w)=5.0×10³ at0.10 M HNO₃ and D_(w)=2.4×10⁵ at 3.0 M HNO₃ for Y(III), whereasN,N,N′,N′-tetra(2-ethylhexyl)-DGA resin affords D_(w)=8.4 in 0.10 M HNO₃and D_(w)=9.3×10⁴ at 3.0 M HNO₃. Above 0.10 M HNO₃, the partitioning ofthese trivalent cations by N,N,N′,N′-tetra-(2-ethylhexyl)-DGA resinexhibits an acid dependence of approximately three, which is consistentwith the extraction of trivalent cations by neutral extractants. Thisbehavior contrasts with that observed in FIG. 5 forN,N,N′,N′-tetra-n-octyl-DGA resin, in which the slope over the 0.1–2 Mrange of HNO₃ is approximately two. Also noteworthy is the plateau inD_(w) exhibited by the N,N,N′,N′-tetra-n-octyl derivative aboveapproximately 2 M HNO₃, whereas partitioning byN,N,N′,N′-tetra-(2-ethylhexyl)-DGA increases steadily to the highestHNO₃ concentration of 8.0 M used in these studies.

The acid dependence for N,N,N′,N′-tetra-(2-ethylhexyl)-DGA shown in FIG.9 illustrates the feasibility of stripping loaded solutes using diluteHNO₃. This behavior is substantially different from that exhibited bythe N,N,N′,N′-tetra-n-octyl-DGA derivative (FIG. 5) in which retentionof some cations in dilute HNO₃ is still significant. These resultsexpand the utility of the DGA resins to those processes than cannottolerate HCl as a stripping agent.

The overall S^(Y) _(Ce) in 3.0 M HNO₃ is somewhat larger at 58 forN,N,N′,N′-tetra-n-octyl-DGA resin than forN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin with S^(Y) _(Ce)=33.Interestingly, the S^(Y) _(Eu) values from 3.0 M HNO₃ are nearlyequivalent at 10 and 12 for the N,N,N′,N′-tetra-n-octyl-DGA andN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resins, respectively.

FIG. 10 shows the HCl acid dependence for the same three cations usingN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, and these results are similarto those obtained for its straight chain n-octyl analog (FIG. 6). TheD_(w) values for these cations with the N,N,N′,N′-tetra-n-octyl-DGA andN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resins decrease to less thanapproximately 20 at 0.10 M HCl, which illustrates the utility of theseseparation media for loading in concentrated HNO₃ (or HCl) and strippinginto dilute HCl solutions.

Although there are significant differences in the extraction propertiesof separation media containing the N,N,N′,N′-tetra-n-octyl-DGA andN,N,N′,N′-tetra-(2-ethylhexyl)-DGA molecules, such behavior cannot beunequivocally attributed to steric effects based on the current data. Inaddition to steric considerations, different HNO₃ extraction behavior,self-aggregation characteristics, and any combination of these variablescan contribute to the unique behavior exhibited by the n-octyl and2-ethylhexyl derivatives of DGA.

EXAMPLE 6 Separation of Ac(III) and Ra(II)

FIG. 11 shows the results of a chromatographic study in which theability of the N,N,N′,N′-tetra-n-octyl-DGA resin to separate Ac(III)from Ra(II) present in 6.0 M HNO₃ is demonstrated. Over 90% of theRa(II) is eluted through the first bed volume of rinse, and moreextensive rinsing affords a better decontamination from Ra(II) in theAc(III) stripping regime. Some breakthrough of Ac(III) is observedduring the 9.5 bed volumes of load; however, these values are barelystatistically significant at just over twice background radiationlevels.

Stripping the N,N,N′,N′-tetra-n-octyl-DGA resin with 0.10 M HCl removes96% of the Ac(III) in just five bed volumes. The stripping peak in FIG.11 shows a maximum decontamination factor (DF) of Ac(III) from Ra(II) ofmore than 10², although more extensive rinsing is likely to increase theDF to more than 10⁴.

EXAMPLE 7 Further Separation Studies

Table 3 summarizes the results of another chromatographic studyinvolving a separation medium comprised of N,N,N′,N′-tetra-n-octyl-DGAcoated on an inert resin (Amberchrom® CG-71, as discussed previously)and a variety of analytes. During the load phase, ≧90% of Ba(II),Cd(II), Cu(II), and Fe(III) elute in 4 M HNO₃, whereas Y(III) and Zr(IV)are strongly retained. Extensive rinsing with 0.5 M HNO₃ elutes theremaining quantities of Ba(II), Cd(II), Cu(II), and Fe(III), with norelease of Y(III) or Zr(IV). Only after four bed volumes of strip with0.01 M HCl is the Y(III) substantially eluted, whereas less than 50% ofthe Zr(IV) is eluted in a broad band covering 10 bed volumes. Theability of N,N,N′,N′-tetra-n-octyl-DGA separation medium to efficientlyseparate Y(III) from Fe(III) is notable, as the latter is ubiquitous inmany analytical and commercially important separations.

TABLE 3 Elution of selected cations on N,N,N′,N′-tetra-n-octyl-DGAresin. Bed Percent of Total Fraction Vols. Ba(II) Cd(II) Cu(II) Fe(III)Y(III) Zr(IV) Load 20 90 93 95 92 0 0.9 (4 M HNO₃) Rinse 2.0 10 7 3.5 70 0.2 (0.5 M 2.0 <0.1 <0.1 0.4 0.6 0 0 HNO₃) 2.0 <0.1 0 0.4 <.1 0 0 2.00 0 0.4 0.4 0 0 2.0 0 0 <0.1 0 0 0 Strip 2.0 0 0 0 0 71 5 (0.01 M 2.0 00 0 0 27 10 HCl) 2.0 0 0 0 0 1 11 2.0 0 0 0 0 0.7 10 2.0 0 0 0 0 0.3 10Column bed volume = 0.5 mL, flow rate = 0.5 mL/minute for load and 0.25mL/minute for wash and strip

Table 4, below, shows the elution behavior of several of the divalentalkaline earth cations on N,N,N′,N′-tetra-n-octyl-DGA resin. During the10 bed volumes of load with 4 M HNO₃, the majority of the Mg(II) andBa(II) elute, whereas Ca(II) and Sr(II) are retained. The remainingMg(II) and Ba(II) are essentially removed with the first bed volume ofrinse with 0.5 M HNO₃, and the Sr(II) is shown to elute under theseconditions. Interestingly, Ca(II) is retained by theN,N,N′,N′-tetra-n-octyl-DGA resin in 0.5 M HNO₃, but elutes in a ratherbroad band in 0.1 M HNO₃. The last vestiges of Ca(II) are removed ineight bed volumes of 0.1 M HCl.

TABLE 4 Elution of selected cations on N,N,N′,N′-tetra-n-octyl-DGA resinPercent of Total Bed Fraction Vols. Mg(II) Ca(II) Sr(II) Ba(II) Load(4 MHNO₃) 10 94 1.1 0 96 Rinse 2 2.6 <0.1 1.2 4 (0.5 M HNO₃) 2 0.5 0 96 0 20.2 0.1 2.4 0 2 0.8 0.2 0.4 0 2 0.5 0.2 <0.1 0 Rinse 2 0.1 28 <0.1 0(0.1 M HNO₃) 2 0.1 63 0 0 2 0.1 3.4 0 0 2 0 1.1 0 0 2 0 1.1 0 0 Strip 40.1 1.1 0 0 (0.1 M HCl) 4 0.1 1.1 0 0 Column bed volume = 0.5 mL, flowrate = 0.5 mL/minute for load and 0.25 mL/minute for wash and strip

Related data for the N,N,N′,N′-tetra-n-octyl-DGA resin have shown thatPb(II) behaves similarly to Sr(II) and that Ra(II) behaves similarly toBa(II). These data show that, under the appropriate solution conditions,divalent cations can be retained by a separation medium comprised ofN,N,N′,N′-tetra-n-octyl-DGA resin and that some intra-alkaline earthseparations can be effected using that separation medium.

Each of the patents and articles cited herein is incorporated byreference. The use of the article “a” or “an” is intended to include oneor more.

The foregoing description and the examples are intended as illustrativeand are not to be taken as limiting. Still other variations within thespirit and scope of this invention are possible and will readily presentthemselves to those skilled in the art.

1. A separation medium comprising a diglycolamide extractantcorresponding in structure to Formula I dispersed onto a porous inertresin or silica support,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 14 to about 56carbon atoms.
 2. The separation medium according to claim 1 wherein saidresin is macroreticular.
 3. The separation medium according to claim 1wherein said tetra-substituted diglycolamide extractant comprises about3 to about 50 weight percent of the total dry weight of the separationmedium.
 4. The separation medium according to claim 1 whereinR¹+R²+R³+R⁴ contains about 16 to about 40 carbon atoms.
 5. A separationmedium comprising a diglycolamide extractant corresponding in structureto Formula I dispersed onto a porous inert resin support, saiddiglycolamide comprising about 3 to about 50 weight percent of the totaldry weight of the separation medium,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 16 to about 40carbon atoms.
 6. The separation medium according to claim 5 wherein eachof R¹, R², R³ and R⁴ is a hydrocarbyl group.
 7. The separation mediumaccording to claim 5 wherein said diglycolamide extractant is presentdissolved in an organic diluent having a boiling point of about 170degrees to about 220 degrees C at atmospheric pressure.
 8. Theseparation medium according to claim 7 wherein said diglycolamideextractant is present at about 0.1 to about 1.5 molar.
 9. The separationmedium according to claim 5 wherein said separation medium is present asfree flowing particles.
 10. The separation medium according to claim 5wherein said diglycolamide extractant is present at about 10 to about 40weight percent of the total dry weight of the separation medium.
 11. Aseparation medium comprising a diglycolamide extractant corresponding instructure to Formula I dispersed onto a porous inert resin support, saiddiglycolamide comprising about 3 to about 50 weight percent of the totaldry weight of the separation medium, said separation medium beingpresent as free flowing particles,

wherein R¹, R², R³ and R⁴ are the same or different hydrocarbyl groupssuch that R¹+R²+R³+R⁴ contains about 16 to about 40 carbon atoms. 12.The separation medium according to claim 11 wherein each of R¹, R², R³and R⁴ is an n-octyl group or a 2-ethylhexyl group.